The present invention relates to a new process which, by allowing the installation of the structures constituting the deck supporting beams, the drilling and production equipment, the living quarters, i.e., the whole complex constituting the complete superstructure of an offshore platform, in enbloc form and with one single positioning operation, allows notable cost and time savings in the laying of platforms in the high seas, as well as providing platforms which are more rational, of immediate functionality, and better optimized and hence less heavy.
It is known that in the installation of an offshore platform, the most critical step is that of mating or depositing the upper structure or deck of the platform which, while being supported by a suitable vessel or transportation raft or barge, is unavoidably subjected to the wave motion of sea, onto the fixed legs, emerging from water, of the platform's lower structure or jacket, which rests on the sea bottom. During this stage, it is desirable to achieve the transferral of the load of the platform's upper structure from barge deck to jacket legs as rapidly as possible to avoid the harmful effects of wave-motion which could damage both the structure and the vessel or raft used to carry the structure.
From the present art a process is already known for installing a platform's deck on jacket legs. According to the known process, the deck, supported by the floating hull of a barge or raft, is positioned by the barge or raft amid jacket legs, and then lowered onto the jacket legs and liberated from the barge or transportation raft by suitably submerging the barge or raft.
Such a process has, however, a number of drawbacks. The main drawback is the very long time required for flooding the ballast tanks of raft or barge, to submerge it. This renders the mating operation very difficult, in that it requires a smooth sea for long time periods since the barge is very sensitive to wave motion. Such a need makes the use of this known process impractical in those areas wherein wave motion is always present. Additionally, since raft submerging inertia does not accomplish the setting down operation as perfectly controlled and prefixed as necessary, no precision can be obtained in the mating operation, which results in many attempts being required and hence considerable efforts and time. Moreover, during these repeated attempts, lasting in time, both the raft or barge and platform superstructure or deck shall suffer many impacts, due to the wave motion, against jacket legs, with consequent possibility of considerable damages to the structures. Finally, since the deck must always be kept at a level higher than the protruding legs of the jacket legs, independently from sea wave motion, a large frame is used to support the deck on the raft, requiring big and expensive transportation rafts, with consequent navigation difficulties.
A further drawback of this known process is that both the very deck, that is to say the structure constituting the platform deck bearing beams, and the other parts constituting the complete superstructure of off shore platform must be transported and installed as modules, resulting in an increase in the cost of installation and the amount of equipment required for installation, as well as the need of further transportation and naval lifting means.